HR: 0830h
AN: H11G-0935    [PDF]
TI: Migration of conservative and sorbing radionuclides in heterogeneous fractured rock aquifers at the Nevada Test Site
AU: * Boryta, J R
EM: jboryta@lanl.gov
AF: Los Alamos National Laboratory, MS-T003, Los Alamos, NM 87545 United States
AU: * Boryta, J R
EM: jboryta@lanl.gov
AF: Dept. of Hydrology, University of Arizona, Tucson, AZ 85721 United States
AU: Wolfsberg, A V
EM: awolf@lanl.gov
AF: Los Alamos National Laboratory, MS-T003, Los Alamos, NM 87545 United States
AB: The Nevada Test Site (NTS) is the United States continental nuclear weapons testing site. The larger underground tests, including BENHAM and TYBO, were conducted at Pahute Mesa. The BENHAM test, conducted in 1968, was detonated 1.4 km below the surface and the TYBO test, conducted in 1975, was detonated at a depth of 765 m. Between 1996 and 1998, several radionuclides were discovered in trace concentrations in a monitoring well complex 273 m from TYBO and 1300 m from BENHAM. Previous studies associated with these measurements have focused primarily on a) plutonium discovered in the observation wells, which was identified through isotopic finger printing as originating at BENHAM, b) colloid-facilitated plutonium transport processes, and c) vertical convection in subsurface nuclear test collapse chimneys. In addition to plutonium, several other non-, weakly-, and strongly-sorbing radionuclides were discovered in trace concentrations in the observation wells, including tritium, carbon-14, chlorine-36, iodine-129, technetium-99, neptunium-237, strontium-90, cesium-137, americium-241, and europium-152,154,155. The range in retardation processes affecting these different radionuclides provides additional information for assessing groundwater solute transport model formulations. For all radionuclides, simulation results are most sensitive to the fracture porosity and fracture aperture. Additionally, for weakly sorbing Np, simulation results are highly sensitive to the matrix sorption coefficient. For strongly sorbing species, migration in the absence of colloids can only be simulated if fracture apertures are set very large, reducing the amount of diffusion that can occur. For these species, colloid-facilitated transport appears to be a more likely explanation for the measurements. This is corroborated with colloid-transport model simulations.
DE: 1040 Isotopic composition/chemistry
DE: 1803 Anthropogenic effects
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2003 Fall Meeting